Chapter 2. Solar Radiation. Terminology & Definitions Geometric & Atmospheric Effects Solar Power & Energy Measurements & Data Jim Dunlop Solar

Transcription

1 Chapter 2 Solar Radiation Terminology & Definitions Geometric & Atmospheric Effects Solar Power & Energy Measurements & Data 2012 Jim Dunlop Solar

2 Overview Defining basic terminology associated with solar radiation, including solar irradiance (power), solar irradiation (energy) and peak sun hours. Identifying the instruments used for measuring solar radiation. Understanding the effects of the earth s movements and atmospheric conditions on the solar energy received on the earth s surface. Locating the sun s position using sun path diagrams and defining the solar window. Accessing solar radiation data resources and quantifying the effects of collector orientation on the amount of solar energy received Jim Dunlop Solar Solar Radiation: 2-2

3 Sun - Earth Relationships 93 million miles, average (1.5 x 10 8 km) 1 Astronomical Unit (Distance traveled in 8.31 minutes at the Speed of Light) Sun: Diameter: 865,000 miles (1,392,000 km, 109 times earth) Mass: 2 x kg (330,000 times earth) Density: 1.41 g/cm 3 Gravity: 274 m/s 2 (28 g) Surface Temperature: 10,000 F (5800 K) Earth: Diameter: 7,930 miles (12,756 km) Mass: 5.97 x kg Density: 5.52 kg/cm 3 Gravity: 9.81 m/s 2 (1 g) Typical Surface Temperature: 68 F (300K) Earth s Orbit Around Sun: 1 year Earth s Rotation about its Polar Axis: 1 day 2012 Jim Dunlop Solar Solar Radiation: 2-3

4 Solar Radiation Solar radiation is electromagnetic radiation ranging from about 0.25 to 4.5 µm in wavelength, including the near ultraviolet (UV), visible light, and near infrared (IR) radiation. NASA Common units of measure for electromagnetic radiation wavelengths: 1 Angstrom (Å) = meter (m) 1 nanometer (nm) = 10-9 meter 1 micrometer (µm) = 10-6 meter 1 millimeter (mm) = 10-3 meter 1 kilometer (km) = 1000 meters 2012 Jim Dunlop Solar Solar Radiation: 2-4

5 Electromagnetic Spectrum Gamma rays Wavelength 1 Å 10 Å 100 Å 0.1 µm 1 µm 10 µm 100 µm 1 mm 10 mm 100 mm 1 m 10 m 100 m 10 3 m 10 4 m 10 5 m X rays Ultraviolet Radiation Visible Light Infrared Radiation Microwaves Short Radio Waves (FM/TV) AM Radio Long Radio Waves 0.25 µm Solar spectrum Visible light 4.5 µm near ultra-violet Wavelength (µm) near infra-red 2012 Jim Dunlop Solar Solar Radiation: 2-5

6 Solar Irradiance (Solar Power) Solar irradiance is the sun s radiant power, represented in units of W/m 2 or kw/m 2. The Solar Constant is the average value of solar irradiance outside the earth s atmosphere, about 1366 W/m 2. Typical peak value is 1000 W/m 2 on a terrestrial surface facing the sun on a clear day around solar noon at sea level, and used as a rating condition for PV modules and arrays. 1 m One Square Meter Typical peak value per m watts = 1 kilowatt 1 m 2012 Jim Dunlop Solar Solar Radiation: 2-6

7 Solar Irradiance For south-facing fixed surfaces, solar power varies over the day, peaking at solar noon. Solar Irradiance (W/m 2 ) Sunrise Noon Sunset Time of Day 2012 Jim Dunlop Solar Solar Radiation: 2-7

8 Solar Irradiation (Solar Energy) Solar irradiation is the sun s radiant energy incident on a surface of unit area, expressed in units of kwh/m 2. Typically expressed on an average daily basis for a given month. Also referred to as solar insolation or peak sun hours. Solar irradiation (energy) is equal to the average solar irradiance (power) multiplied by time. Peak sun hours (PSH) is the average daily amount of solar energy received on a surface. PSH are equivalent to: The number of hours that the solar irradiance would be at a peak level of 1 kw/m 2. Also the equivalent number of hours per day that a PV array will operate at peak rated output levels at rated temperature Jim Dunlop Solar Solar Radiation: 2-8

9 Solar Power and Solar Energy Solar Irradiance (W/m 2 ) Solar irradiation (energy) is the area under the solar irradiance (power) curve Solar irradiance (power) Sunrise Noon Sunset Time of Day 2012 Jim Dunlop Solar Solar Radiation: 2-9

10 Peak Sun Hours Solar Irradiance (W/m 2 ) 1000 W/m 2 Area of box equals area under curve Peak Sun Hours Solar Insolation Solar Irradiance Sunrise Noon Sunset Time of Day (hrs) 2012 Jim Dunlop Solar Solar Radiation: 2-10

11 Solar Power and Energy: Examples The solar power incident on a surface averages 400 W/m 2 for 12 hours. How much solar energy is received? 400 W/m 2 x 12 hours = 4800 Wh/m 2 = 4.8 kwh/m 2 = 4.8 PSH The amount of solar energy collected on a surface over 8 hours is 4 kwh/m 2. What is the average solar power received over this period? 4 kwh/m 2 / 8 hours = 0.5 kw/m 2 = 500 W/m 2 A PV system produces 6 kw AC output at peak sun and average operating temperatures. How much energy is produced from this system per day if the solar energy received on the array averages 4.5 peak sun hours? 6 kw x 4.5 hours/day = 27 kwh/day 2012 Jim Dunlop Solar Solar Radiation: 2-11

12 Atmospheric Effects Approximately 30% of extraterrestrial solar power is absorbed or reflected by the atmosphere before reaching the earth s surface. Effects vary significantly with altitude, latitude, time of day and year, air pollutants, weather patterns and wavelength of solar radiation. Direct beam (normal) radiation is the component of total global solar radiation incident on a surface normal to the sun s rays, that travels in parallel lines directly from the sun. Diffuse radiation is the component of the total global solar radiation incident on a surface that is scattered or reflected. May also include ground reflected radiation (albedo). Total global solar radiation is comprised of the direct, diffuse and reflected components (albedo) Jim Dunlop Solar Solar Radiation: 2-12

13 Atmospheric Effects Sun Parallel rays from sun Solar Constant = 1366 W/m 2 Reflection Outer Limits of Atmosphere Atmospheric Absorption, Scattering and Reflections Cloud Reflections Diffuse Radiation Direct Radiation Diffuse Radiation Reflected (Albedo) Radiation Earth s Surface TOTAL GLOBAL SOLAR RADIATION - DIRECT + DIFFUSE 2012 Jim Dunlop Solar Solar Radiation: 2-13

14 Air Mass Sun directly overhead (zenith) Air Mass = 0 (AM0) Zenith Angle θ z = 48.2 deg Sun at mid-morning or mid-afternoon Horizon Air Mass = 1 (AM1.0) Air mass is calaculated by the following: Earth s Surface Limits of Atmosphere Earth Air Mass = 1.5 (AM1.5) 1 P AM = cosθ z P o where AM = air mass θz = zenith angle (deg) P = local pressure (Pa) Po = sea level pressure (Pa) 2012 Jim Dunlop Solar Solar Radiation: 2-14

15 Measuring Zenith and Altitude Angles Sun Zenith Angle: Length of shadow (l) Tan θz = Height of ruler (h) θz = arctan (l/h) Vertical Altitude Angle: Height of ruler (h) Tan α = Length of shadow (l) α = arctan (h/l) Zenith Angle θ z α Altitude Angle θ z Height of stake or ruler (h) Horizontal Plane Length of shadow (l) 2012 Jim Dunlop Solar Solar Radiation: 2-15

16 U.S. Solar Radiation Data 2012 Jim Dunlop Solar Solar Radiation: 2-16 NREL

19 Solar Spectral Irradiance Spectral Solar Irradiance 2500 Extraterrestrial (AM0) Spectral Irradiance (W m -2 µm -1 ) Terrestrial Total Global (AM1.5) Terrestrial Direct Normal (AM1.5) Aborbed by water vapor Aborbed by CO 2 and water vapor Wavelength (µm) 2012 Jim Dunlop Solar Solar Radiation: 2-19

20 Solar Radiation Measurements A pyranometer measures total global solar irradiance (solar power). Measurements over time are integrated to calculate the total solar irradiation (solar energy) received. Irradiance measurements are used in the field to translate the actual output of PV array and systems to a reference condition and verify performance with expectations. Small inexpensive meters using calibrated PV cells as sensors are available from $150 and up. A small PV module with calibrated short-circuit current can also be used to approximate solar radiation levels Jim Dunlop Solar Solar Radiation: 2-20

21 Precision Spectral Pyranometer (PSP) A pyranometer measures broadband global solar radiation (direct and diffuse) with a thermopile. Used for precision laboratory measurements and weather stations. NREL, Steve Wilcox Dual glass domes improve low incidence angle and thermal accuracy. $$$$ 2012 Jim Dunlop Solar Solar Radiation: 2-21

22 Normal Incidence Pyrheliometer (NIP) A pyrheliometer measures the direct normal component of total global solar radiation. Instrument must always track the sun. Sensor is located at the back of a long tube with a field of view of the width of the solar disk. $$$$$ NREL/Tom Stoffer 2012 Jim Dunlop Solar Solar Radiation: 2-22

23 Photovoltaic Reference Cell A reference cell is a small PV device used to measure solar irradiance. Calibrated current output is proportional to solar irradiance. Used for measuring solar radiation for PV cell or module performance in indoor simulators. PV Measurements, Inc Jim Dunlop Solar Solar Radiation: 2-23

24 LI-COR LI200 Pyranometer Silicon pyranometers use a calibrated PV device to measure solar radiation. Meter sets instrument calibration, averages and integrates solar irradiance. Ideal for field use and long-term system performance monitoring. $$$ 2012 Jim Dunlop Solar Solar Radiation: 2-24

25 Daystar Solar Meter Handheld solar meters use a small PV cell to measure solar irradiance. Careful alignment with plane of array required for accurate measurements. Low cost, good for basic field measurements. $$$ 2012 Jim Dunlop Solar Solar Radiation: 2-25

26 Seaward Solar Solar Survey 100/200R Measures and records solar irradiance, ambient and PV module temperatures, array orientation and tilt angles. 200R features wireless connectivity with the PV150 Solar Installation tester, built-in data logger and USB interface. See: Jim Dunlop Solar Solar Radiation: 2-26

27 Sun-Earth Geometric Relationships Two major motions of the earth affect the solar radiation received on a surface at any location: The rotation of the earth about its polar axis defines a day. The orbit of the earth around the sun defines a year. The amount of solar radiation received at any location on earth depends on the time of day and year, the local latitude, and the orientation of the surface. Also significantly affected by weather conditions Jim Dunlop Solar Solar Radiation: 2-27

28 Earth s Orbit The ecliptic plane is the earth s orbital plane around the sun. The equatorial plane is the plane containing the earth s equator and extending outward into space. The earth s annual orbit around the sun is slightly elliptical. Perihelion is the earth s closest approach to the sun in its orbit, which is about 90 million miles and occurs around January 3. Aphelion is the earth s furthest distance to the sun in its orbit, which is about 96 million miles and occurs around July 4. One Astronomical Unit (AU) is the average sun-earth distance, which is approximately 93 million miles Jim Dunlop Solar Solar Radiation: 2-28

29 Earth s Orbit Around the Sun Summer Solstice: June 20 / 21 Declination = Ecliptic Plane Vernal Equinox: March 20 / 21 Declination = 0 Aphelion: July million miles (1.017 AU) 90 million miles (0.983 AU) Perihelion: January 2-5 Sun Winter Solstice: December 21 / 22 Declination = ( ) Autumnal Equinox: September 22 / 23 Declination = Jim Dunlop Solar Solar Radiation: 2-29

30 Earth s Polar Axis Tilt The earth s polar rotational axis is tilted at a constant 23.5 angle with respect to the ecliptic plane. During its annual orbit around the sun, the earth's polar axis is never perpendicular to the ecliptic plane, but it is always inclined to it at the same angle, This results in a constantly varying angle between the earth s equatorial plane and the ecliptic plane as the earth orbits the sun over a year. Except at the equinoxes, the earth s axis is tilted either toward or away from the sun, causing the change in seasons Jim Dunlop Solar Solar Radiation: 2-30

31 Solar Declination Solar declination (δ) is the angle between the earth s equatorial plane and the sun s rays. Solar declination varies continuously in a sinusoidal fashion over the year due the earth s nearly circular orbit around the sun. Solar declination varies from 23.5 to +23.5, and defines the limits of sun position in the sky relative to any point on earth Jim Dunlop Solar Solar Radiation: 2-31

32 Solar Declination Arctic Circle (66.5 N) North Pole Tropic of Cancer (23.5 N) Equator Ecliptic Plane Tropic of Capricorn (23.5 S) 23.5 Solar Declination Sun s Rays Antarctic Circle (66.5 S) 2012 Jim Dunlop Solar Solar Radiation: 2-32

33 Solar Declination Solar Declination Summer Solstice June 21 Solar Declination (deg) 10 0 (10) Vernal Equinox March 21 Autumnal Equinox September 22 (20) Winter Solstice December 21 (30) Julian Day (1-365) 2012 Jim Dunlop Solar Solar Radiation: 2-33

34 The Solstices The solstices define the points in earth s orbit around the sun having maximum and minimum solar declination. The solstices occur when the earth s axis is inclined at the greatest angle either toward or away from the sun, and defines the annual range of sun position relative to any point on earth. The winter solstice occurs on December 21 or 22 when solar declination is at its minimum (-23.5 ) and the Northern Hemisphere is tilted away from sun. The summer solstice occurs on June 21 or 22 when solar declination is at its maximum (23.5 ), and the Northern Hemisphere is tilted towards the sun Jim Dunlop Solar Solar Radiation: 2-34

35 The Equinoxes The equinoxes define the two points in earth s orbit around the sun having zero solar declination. On the equinoxes, the earth s axis is neither tilted toward or away from the suns rays, but is perpendicular. The sun rises and sets due east and west, respectively, and days and nights equal length (12 hours) everywhere on earth. The sun is directly overhead at solar noon on the equator (at zenith). The vernal equinox occurs on March 20 / 21. Days become longer than nights in Northern Hemisphere for next six months. The autumnal equinox occurs on September 22 / 23. Days become shorter than nights in the Northern Hemisphere for next six months Jim Dunlop Solar Solar Radiation: 2-35

36 Winter Solstice North Pole Arctic Circle (66.5 N) Tropic of Cancer (23.5 N) 23.5 Ecliptic Plane Sun s Rays Equator Tropic of Capricorn (23.5 S) Antarctic Circle (66.5 S) 2012 Jim Dunlop Solar Solar Radiation: 2-36

37 Vernal Equinox North Pole Titled Backward Tropic of Cancer (23.5 N) Equator 23.5 Ecliptic Plane Sun s Rays Tropic of Capricorn (23.5 S) Antarctic Circle (66.5 S) 2012 Jim Dunlop Solar Solar Radiation: 2-37

38 Summer Solstice Arctic Circle (66.5 N) North Pole Tropic of Cancer (23.5 N) Equator Ecliptic Plane Tropic of Capricorn (23.5 S) 23.5 Sun s Rays Antarctic Circle (66.5 S) 2012 Jim Dunlop Solar Solar Radiation: 2-38

39 Autumnal Equinox North Pole Tilted Forward Arctic Circle (66.5 N) Tropic of Cancer (23.5 N) Ecliptic Plane Equator 23.5 Sun s Rays Tropic of Capricorn (23.5 S) 2012 Jim Dunlop Solar Solar Radiation: 2-39

40 Solar Time Apparent solar time is based on the interval between daily sun crossings above a local meridian. Apparent solar time can be measured by a sundial. Mean solar time is based on the average position of the sun assuming the earth rotates and orbits at constant rates. The equation of time (EOT) is the difference between mean and apparent solar time. EOT varies annually with apparent time ahead of mean solar time by about 16.5 min on November 3, or behind by about 14 min on February 12. Due to changing speed of earth at points in elliptical orbit around sun Jim Dunlop Solar Solar Radiation: 2-40

41 Equation of Time Equation of Time Equation of Time (min) (5) (10) Vernal Equinox March 21 Summer Solstice June 21 Autumnal Equinox September 22 Winter Solstice December 21 (15) (20) Julian Day (1-365) 2012 Jim Dunlop Solar Solar Radiation: 2-41

42 Standard Time and Time Zones Coordinated Universal Time (UTC) is based on an atomic clock and mean solar time at the Royal Observatory in Greenwich, London, UK. The prime meridian passes through Greenwich and is arbitrarily taken as 0 longitude. Standard time is based on sun crossing reference meridians or geographical boundaries, generally separated by 15 of longitude. Local standard time is referenced to UTC Eastern Standard Time is UTC-5 hours (UTC-4 during Daylight Savings Time) UTC varies from local solar time by as much as +/- 45 min depending on the day of year, whether Daylight Savings Time is in effect, and longitude of the specific location with respect to the reference time zone meridian Jim Dunlop Solar Solar Radiation: 2-42

43 U.S. Time Zones Alaska UTC-9 UTC with no Daylight Savings Time Hawaii UTC-10 Guan UTC+10 Pacific UTC-8 Mountain UTC-7 Samoa UTC-11 Central UTC-6 Eastern UTC-5 Atlantic UTC-4 NIST/USNO 2012 Jim Dunlop Solar Solar Radiation: 2-43

44 Solar and Standard Time Conversions Example: Determine the local standard time that solar noon occurs on November 3 in Atlanta, GA (33.65 N, W). The adjustment for longitude is determined by: Local standard time of solar noon is determined by: t = ( L L ) 4 L local S where t = longitude time correction (min) L L = local longitude (deg) local L = longitude at standard meridian (deg) S t = t t + t S 0 E L where t = local standard time (hh:mm:ss) S t = solar time (hh:mm:ss) 0 t = Equation of Time (mm:ss) E t = ( ) 4 = 37.7 min = 37:43 mm:ss L t = 12 : 00 : 00 (00 :16 : 30) + (00 : 37 : 43) = 12 : 21:13 EST S 2012 Jim Dunlop Solar Solar Radiation: 2-44

45 Sunlight on Earth Day Near Equinox Night Near Summer Solstice Night Day NIST/USNO 2012 Jim Dunlop Solar Solar Radiation: 2-45

46 The Analemma Analemma 30 Summer Solstice June 21 Jul May 21 Solar Declination (deg) Vernal Equinox March 21 Feb 21 Aug (10) Apr 21 Autumnal Equinox September Oct 21 Jan 21 (20) Nov 21 Winter Solstice December 21 (30) << Sun Slow << Equation of Time (min) >> Sun Fast >> FSEC This Analemma was created by superimposing photographs of the sun taken in the morning at the same clock time, each week of the year, and represents the variation in solar declination and the equation of time over the year Jim Dunlop Solar Solar Radiation: 2-46

47 Sun Position The sun s position in the sky at any moment relative to an observer on earth is defined by two angles. The solar altitude angle (α) is the angle between the sun s rays and the horizon. The solar azimuth angle (θ z ) is the angle between the horizontal projection of a the sun s rays and geographic due south. The zenith angle is the angle between the line to the sun and directly overhead. The zenith and altitude angles are complementary: α + θ z = Jim Dunlop Solar Solar Radiation: 2-47

48 Sun Position Zenith East North Zenith Angle Altitude Angle Horizontal Plane Azimuth Angle West South 2012 Jim Dunlop Solar Solar Radiation: 2-48

49 Sun Path Diagrams at the Equinoxes Zenith 0 Latitude (Equator): Altitude at Solar Noon = 90 N E 23.5 N Latitude (Tropic of Cancer): Altitude at Solar Noon = N Latitude (Seattle, WA): Altitude at Solar Noon = 43 W S 2012 Jim Dunlop Solar Solar Radiation: 2-49

50 Sun Path Diagrams at the Summer Solstice Zenith N E 0 Latitude (Equator): Altitude at Solar Noon = 66.5 (Sun in Northern Sky) 23.5 N Latitude (Tropic of Cancer): Altitude at Solar Noon = 90 (Directly Overhead) 47 Latitude (Seattle, WA): Altitude at Solar Noon = 66.5 (Sun in Southern Sky) W S 2012 Jim Dunlop Solar Solar Radiation: 2-50

51 Sun Path Diagrams at the Winter Solstice Zenith 0 Latitude (Equator): Altitude at Solar Noon = 66.5 E 23.5 N Latitude (Tropic of Cancer): Altitude at Solar Noon = 43 N 47 Latitude (Seattle, WA): Altitude at Solar Noon = 19.5 W S 2012 Jim Dunlop Solar Solar Radiation: 2-51

52 Sun Position on the Equator Sun Position for 0 o Latitude Winter Solstice Summer Solstice Vernal and Autumnal Equinox Altitude Angle (positive above horizon) Noon 11 AM 1 PM 11 AM 10 AM 11 AM Noon 1 PM 2 PM 1 PM 10 AM 10 AM 2 PM 2 PM 8 AM 8 AM 8 AM 4 PM 4 PM 4 PM (30) (60) (90) (120) (150) (180) << East (positive) << Azimuth Angle >> West (negative) >> 2012 Jim Dunlop Solar Solar Radiation: 2-52

53 Sun Position for 15 N Sun Position for 15 o N Latitude Winter Solstice Summer Solstice Vernal and Autumnal Equinox Altitude Angle (positive above horizon) AM 10 AM 8 AM AM Noon 10 AM 11 AM Noon 10 AM 8 AM 8 AM PM 1 PM 2 PM 2 PM 1 PM 2 PM 4 PM 4 PM 4 PM (30) (60) (90) (120) (150) (180) << East (positive) << Azimuth Angle >> West (negative) >> 2012 Jim Dunlop Solar Solar Radiation: 2-53

54 Sun Position for 30 N Sun Position for 30 o N Latitude Winter Solstice Summer Solstice Vernal and Autumnal Equinox Altitude Angle (positive above horizon) AM Noon 10 AM 11 AM Noon 10 AM 8 AM 11 AM 10 AMNoon 8 AM 8 AM PM 2 PM 1 PM 2 PM 4 PM 1 PM 2 PM 4 PM 4 PM (30) (60) (90) (120) (150) (180) << East (positive) << Azimuth Angle >> West (negative) >> 2012 Jim Dunlop Solar Solar Radiation: 2-54

55 Sun Position for 45 N Sun Position for 45 o N Latitude Winter Solstice Summer Solstice Vernal and Autumnal Equinox Altitude Angle (positive above horizon) AM Noon 10 AM 11 AM 8 AM 10 AM Noon 8 AM 11 AM 10 AMNoon 8 AM PM 2 PM 1 PM 2 PM 4 PM 1 PM 2 PM 4 PM 4 PM (30) (60) (90) (120) (150) (180) << East (positive) << Azimuth Angle >> West (negative) >> 2012 Jim Dunlop Solar Solar Radiation: 2-55

56 Sun Position for 60 N Sun Position for 60 o N Latitude Winter Solstice Summer Solstice Vernal and Autumnal Equinox Altitude Angle (positive above horizon) AM 8 AM AM 10 AM Noon 11 AM 10 AM Noon 11 AM 10 AM Noon PM 2 PM 4 PM 1 PM 2 PM 4 PM 1 PM 2 PM (30) (60) (90) (120) (150) (180) << East (positive) << Azimuth Angle >> West (negative) >> 2012 Jim Dunlop Solar Solar Radiation: 2-56

57 Sun Position for 75 N Sun Position for 75 o N Latitude Winter Solstice Summer Solstice Vernal and Autumnal Equinox Altitude Angle (positive above horizon) AM 8 AM AM11 AM Noon 10 AM11 AM Noon PM2 PM 4 PM 1 PM2 PM 4 PM (30) (60) (90) (120) (150) (180) << East (positive) << Azimuth Angle >> West (negative) >> 2012 Jim Dunlop Solar Solar Radiation: 2-57

58 The Solar Window The solar window represents the range of sun paths for a given latitude between the winter and summer solstices. As latitudes increase from equator: The solar window is inclined at a closer angle with the southern horizon. Sun path and days are longer during summer; shorter during winter. For any location, the maximum altitude of the sun at solar noon varies 47 between the winter and summer solstice. PV arrays should be oriented toward the unobstructed solar window for maximum solar energy collection Jim Dunlop Solar Solar Radiation: 2-58

59 Solar Window on the Equator Winter Solstice Zenith Equinoxes Summer Solstice 47 E N W S 2012 Jim Dunlop Solar Solar Radiation: 2-59

60 Solar Window on the Tropic of Cancer (23.5 N) Winter Solstice Zenith Equinoxes Summer Solstice 47 E N W S 2012 Jim Dunlop Solar Solar Radiation: 2-60

61 Solar Window in Seattle, WA (47 N) Winter Solstice Zenith Equinoxes Summer Solstice E N 47 W S 2012 Jim Dunlop Solar Solar Radiation: 2-61

62 Collector Orientation The orientation of PV arrays and other solar collectors is defined by two angles with respect to the earth s surface. The collector azimuth angle represents the angle between due geographic south and direction the collector faces. The collector tilt angle represents the angle the array surface makes with the horizontal plane. The solar incidence angle represents the angle between the sun s rays and the normal (perpendicular) to a collector surface Jim Dunlop Solar Solar Radiation: 2-62

63 Array Orientation Zenith Surface Normal North - 0 Solar Incidence Angle East - 90 Collector Tilt Angle Horizontal Plane Collector Azimuth Angle West Surface Direction South Jim Dunlop Solar Solar Radiation: 2-63

64 Optimal Collector Orientation Maximum annual solar energy is received on a fixed surface that faces due south, and is tilted from the horizontal at an angle slightly less than local latitude. Fall and winter performance is enhanced by tilting collectors at angles greater than latitude. Spring and summertime performance is enhanced by tilting collectors at angles lower than latitude. For the central and southern U.S., latitude-tilt surfaces with azimuth orientations of ± 45 degrees from due south and with tilt angles ± 15 of local latitude will generally receive 95 % or more of the annual solar energy received on optimally-tilted south-facing surfaces Jim Dunlop Solar Solar Radiation: 2-64

65 Effect of Collector Tilt Angle on Solar Energy Received Orlando, FL Predicted Insolation on South-Facing Tilted Surfaces 9 Insolation (kwh/m 2 -day) H (0 deg) H (15 deg) H (30 deg) H (45 deg) 3 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month 2012 Jim Dunlop Solar Solar Radiation: 2-65

66 Effects of Collector Tilt and Azimuth on Annual Solar Energy Received Miami, FL Boston, MA Available Irradiation (% of maximum) Available Irradiation (% of maximum) Tilt (deg) Tilt (deg) Azimuth (deg) Azimuth (deg) 2012 Jim Dunlop Solar Solar Radiation: 2-66

67 Solar Radiation Resource Data Available from National Renewable Energy Laboratory (NREL) - Renewable Resource Data Center (RReDC): Includes extensive collection of renewable energy data, maps, and tools for using biomass, geothermal, solar, and wind resources. Solar resource data is used for sizing and estimating the performance of solar energy utilization systems Jim Dunlop Solar Solar Radiation: 2-67

68 National Solar Radiation Database NSRDB years of solar radiation and meteorological data from 239 NWS sites in the U.S. TMY2 hourly data files NSRDB Update Contains solar and meteorological data for 1,454 sites. TMY3 hourly data files NREL 2012 Jim Dunlop Solar Solar Radiation: 2-68

69 Solar Radiation Data Tables Standard format spreadsheets provide minimum and maximum data for each month and annual averages for: Total global solar radiation for fixed south-facing flat-plate collectors tilted at angles of 0, Lat-15, Lat, Lat+15 and 90. Total global solar radiation for single-axis, north-south tracking flat-plate collectors at tilt angles of 0, Lat-15, Lat and Lat+15. Total global solar radiation for dual-axis tracking flat-plate collectors. Direct beam radiation for concentrating collectors. Meteorological data Jim Dunlop Solar Solar Radiation: 2-69

70 Solar Radiation Data Tables City: DAYTONA BEACH State: FL WBAN No: Lat(N): Long(W): Elev(m): 12 Pres(mb): 1017 Stn Type: Primary SOLAR RADIATION FOR FLAT-PLATE COLLECTORS FACING SOUTH AT A FIXED-TILT (kwh/m2/day), Percentage Uncertainty = 9 Tilt(deg) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year 0 Average Minimum Maximum Lat - 15 Average Minimum Maximum Lat Average Minimum Maximum Lat + 15 Average Minimum Maximum Average Minimum Maximum NREL 2012 Jim Dunlop Solar Solar Radiation: 2-70

71 Sun-Tracking Arrays Two-Axis Tracking Vertical-Axis Tracking East-West Tracking Optional seasonal adjustment Optional seasonal adjustment North West East 2012 Jim Dunlop Solar Solar Radiation: 2-71 South

72 Solar Radiation Data Tables City: DAYTONA BEACH State: FL WBAN No: Lat(N): Long(W): Elev(m): 12 Pres(mb): 1017 Stn Type: Primary SOLAR RADIATION FOR 1-AXIS TRACKING FLAT-PLATE COLLECTORS WITH A NORTH-SOUTH AXIS (kwh/m2/day), Percentage Uncertainty = 9 Axis Tilt Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year 0 Average Minimum Maximum Lat - 15 Average Minimum Maximum Lat Average Minimum Maximum Lat + 15 Average Minimum Maximum SOLAR RADIATION FOR 2-AXIS TRACKING FLAT-PLATE COLLECTORS (kwh/m2/day), Percentage Uncertainty = 9 Tracker Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year 2-Axis Average Minimum Maximum NREL 2012 Jim Dunlop Solar Solar Radiation: 2-72

73 Solar Radiation Data Tables City: DAYTONA BEACH State: FL WBAN No: Lat(N): Long(W): Elev(m): 12 Pres(mb): 1017 Stn Type: Primary DIRECT BEAM SOLAR RADIATION FOR CONCENTRATING COLLECTORS (kwh/m2/day), Percentage Uncertainty = 8 Tracker Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year 1-X, E-W Average Hor Axis Minimum Maximum X, N-S Average Hor Axis Minimum Maximum X, N-S Average Tilt=Lat Minimum Maximum X Average Minimum Maximum AVERAGE CLIMATIC CONDITIONS Element Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Temp. (deg C) Daily Min (deg C) Daily Max (deg C) Record Lo (deg C) Record Hi (deg C) HDD,Base= 18.3C CDD,Base= 18.3C Rel Hum percent Wind Spd. (m/s) NREL 2012 Jim Dunlop Solar Solar Radiation: 2-73

74 PVWATTS Performance Calculator Used to evaluate solar energy collected and the performance of grid-tied PV systems for any array azimuth and tilt angles. User selects state and city from map, and enters size of PV system, array orientation and derating factors. Results give monthly and annual solar energy received and PV system AC energy production. NREL 2012 Jim Dunlop Solar Solar Radiation: 2-74

75 PVWATTS Output 2012 Jim Dunlop Solar Solar Radiation: 2-75 NREL

76 Summary The solar radiation received on earth is affected by the earth s movements and atmospheric conditions. Solar irradiance (power) is expressed in units of W/m 2 or kw/m 2, and measured with a pyranometer. Typical peak values are around 1000 W/m 2 on a surface at sea level facing the sun around solar noon; used as the rating condition for PV modules and arrays. Solar irradiation (energy) is solar power integrated over time, expressed in units of kwh/m 2 /day. Solar energy resource data are used in sizing and estimating the performance of PV systems, and varies location and with collector orientation. The solar window defines the range of sun paths between the winter and summer solstices for a specific latitude. PV arrays are oriented toward the solar window for maximum energy gain Jim Dunlop Solar Solar Radiation: 2-76

77 Questions and Discussion 2012 Jim Dunlop Solar Solar Radiation: 2-77